Photocatalytic Gas Phase Reactions

Photocatalytic gas phase reactions represent a less explored yet promising direction within the highly active research area of photocatalysis. While photocatalytic liquid phase reactions are typically performed in water, photocatalytic gas phase reactions focus on gaseous and vaporized compounds. With this change in reaction environment, it is possible to address completely new questions and topics. Examples lie in the field of solar fuels, air pollution, global warming, and green chemistry. For this review, we selected five photocatalytic gas phase reactions, namely the reduction of CO2, water splitting, the oxidation of volatile organic compounds, the degradation of nitrogen oxides, and the synthesis of ammonia, which we discuss in the context of why they are important from a scientific, technological, and also societal point of view. We present the chemical mechanisms behind these photocatalytic processes and propose ideas and strategies for how these processes can be made more efficient. Our literature survey results in a list of 11 points regarding how the selectivity and yield of photocatalytic gas phase reactions can be increased by optimizing the composition of the photocatalysts, their surface chemistry, and experimental parameters such as temperature, gas flow, and gas composition.